Generally, there has been a method in which a straight line is divided by a predetermined interval upon which a linear interpolation of a robot movement and a point-to-point (PTP) movement is executed. The PTP movement is executed by taking a very small distance of a straight line and driving the robot along a path of said divided straight line. However, this method has had a problem in that the precision of the rectilinear movement is reduced at the driving start and the driving end of the robot movement.
A position determining control system disclosed in Japanese Laid-Open Patent Publication Showa 62-62363 can be cited as a concrete, conventional example. However, this position determining control system involves making a position determination of high precision in a position determining control system, which corrects an error in a movement control amount at a check point. This system comprises a first means which recognizes a present position of a moving means on the basis of the moving means and a tacho-pulse output from a motor for moving the robot within a coordinate system. The system controls the driving of said motor in accordance with the result of the first means. The system also determines the position of the moving means relative to a target position on the coordinates system. A second means reads a position signal of a wider width than the tacho-pulse from the coordinate system when the moving means passes a particular check point on the coordinate system. This system further includes a third means which amends a result of recognition of the present position of the moving means by the first means by applying an intermediate point in a position signal read by the second means, as a positional reference. The third means corrects a difference between an actual position and the present position of the moving means recognized by the first means every time the moving means passes the check point.
Such a conventional system has had an advantage in that a square pulse of relatively wider width is used as a position signal and a deviation is detected by applying the intermediate point of the position signal as a positional reference signal. However, it has had a disadvantage in that not only it is not effective for driving a robot a short distance (despite it being useful for a robot which drives for a relatively long distance), but the acceleration or deceleration in response to a situation is impossible and also a high speed operation is impossible.
Japanese Laid-Open Patent Publication Showa 57-211491 can be also cited, wherein the system is constituted such that an object of a robot body to be controlled is moved at a predetermined speed between a plurality of predetermined pass-through positions. A track is controlled so as to be smoothly moved while automatically accelerating/decelerating following a parabola by adopting the same rectilinear speed as a rectilinear speed on an inscribing parabola, which is determined by an error quantity of the pass-through position in the vicinity of said position and by a previously set position at the vicinity of the position, so that an operator can voluntarily presume the error quantity corresponding to passing through the particular vicinity. Thereby, the pass-through points can be continuously moved with a smooth speed without stopping at every respective pass-through point, and thus a desirable-movement performance without vibration at the pass-through point is obtained.
However, such conventional position control system has had problems in that there are so many structural elements of the device for realizing the position control, and the positional error amount is voluntarily presumed by an operator. Accordingly, not only an error operation for the position control, which requires a high precision, is necessary, but also a high speed movement is impossible.